With the acceleration of the adoption of the use of smart phones, various application services using the smart phone are being activated and such an aspect of smart phone use is expected to be accelerated more and more in the future. Accordingly, various technologies have arisen to effectively prevent data congestion due to the various application services in a cellular system. For example, according to the use of high capacity mobile contents, a Device to Device (D2D) communication to efficiently distribute loads of a base station by using proximity of mobile communication terminals is spotlighted. The D2D communication is being standardized by the 3rd Generation Partnership Project (3GPP) Radio Access Network (RAN) Technical Specification Group (TSG).
The D2D communication which forms and maintains a D2D communication network by allowing terminals to distributively use limited radio resources, without assistance of the network such as from the base station, may include operations including synchronization, peer discovery, paging, data traffic communication, and the like. In the synchronization operation, basic time and frequency are synchronized between terminals through a Global Positioning System (GPS) or the like. In the peer discovery operation, each terminal identifies geographically proximate neighboring terminals through broadcast terminal information. In the paging operation, a D2D link for unidirectional transmission between terminals which desire communication is formed. In the traffic communication operation, link scheduling and data transmission according to the link scheduling are performed based on the formed link through the above operations.
A D2D Proximity Service (ProSe) may be largely classified into a D2D discovery and direct communication. The D2D discovery refers to a process in which a particular terminal recognizes another terminal located near the terminal. The direct communication refers to a process in which terminals directly communicate with each other without passing through the base station, unlike the conventional cellular system in which the terminals communicate with each other via the base station.
The D2D communication may be classified into a network communication and a direct communication. Further, the D2D discovery may be classified into a network discovery and a direct discovery.
In the network communication (or discovery), the network (or base station) is involved in a series of all processes related to a communication (discovery) of the terminal That is, the base station may dynamically allocate a chunk of resources required for the communication (discovery) in every scheduling period and the network is involved in the communication (discovery) in a centralized manner in which the base station selects Resource Blocks (RBs) to be used by terminals which actually transmit/receive communication (discovery) signals.
Meanwhile, in the direct communication (discovery), a role of the network is minimized. That is, the base station statically allocates a chunk of resources required for the communication (discovery) and terminals to perform the communication (discovery) within the allocated chunk of resources select RBs required for the communication (discovery) in a distributed manner and transmit communication (discovery) signals.
Each terminal is required to transmit the communication (discovery) signal for the direct communication (discovery). Terminals which desire to transmit the communication (discovery) signal select one or more RBs from the RBs existing in a corresponding subframe and transmit the communication (discovery) signal. Since each terminal does not know which terminal transmits which signal, the terminal is required to select a resource for transmitting the communication (discovery) signal before transmitting the communication (discovery) signal.
A Greedy approach may be applied as an example of a method of selecting an RB for direct communication (discovery) signal transmission. The Greedy approach corresponds to a method in which the User Equipment (UE) receives communication (discovery) signals for a predefined communication (discovery) interval, measures energy levels of all RBs within the communication (discovery) interval, and randomly selects one of the RBs which has an energy level within the bottom x % (for example, 5%). The terminal transmits the communication (discovery) signal to the selected RB.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.